https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99287
Patrick Palka <ppalka at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Assignee|unassigned at gcc dot gnu.org |ppalka at gcc dot
gnu.org
Status|NEW |ASSIGNED
--- Comment #3 from Patrick Palka <ppalka at gcc dot gnu.org> ---
IIUC, those two types are actually the same, it's just that one of them was
obtained through the char_type alias, and it seems debug_tree prefers to show
the name of the alias when the type came from one.
It seems the issue ultimately is in cxx_eval_increment_expression: during
evaluation of ++__first with __first = &"mystr"[n] + m and with lval=false,
since cxx_fold_pointer_plus_expression and not fold_build2 is responsible for
simplifying this POINTER_PLUS_EXPR to &"mystr"[n+m], returning 'mod' actually
returns the unreduced &"mystr"[n] + m rather than the reduced &"mystr"[n+m]
that we obtain as part of constexpr evaluation of the temporary MODIFY_EXPR.
This unreduced return value of cxx_eval_increment interfers with later
constexpr evaluation, e.g. folding of the POINTER_DIFF_EXPR.
I'm testing the following which updates 'mod' with the result of evaluation of
the MODIFY_EXPR:
--- a/gcc/cp/constexpr.c
+++ b/gcc/cp/constexpr.c
@@ -5582,20 +5582,14 @@ cxx_eval_increment_expression (const constexpr_ctx
*ctx, tree t,
/* Storing the modified value. */
tree store = build2_loc (cp_expr_loc_or_loc (t, input_location),
MODIFY_EXPR, type, op, mod);
- cxx_eval_constant_expression (ctx, store,
- true, non_constant_p, overflow_p);
+ mod = cxx_eval_constant_expression (ctx, store, false,
+ non_constant_p, overflow_p);
ggc_free (store);
/* And the value of the expression. */
